The background information is believed, at the time of the filing of this patent application, to adequately provide background information for this patent application. However, the background information may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the background information are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
Headspace sampling devices and systems typically comprise a vial configured to receive and hold a sample and for the introduction of a sparging or inert gas through the vial. The gas carries headspace vapor from the vial to an analytical device. Typical sampling devices may have a vial sealed with a diaphragm or septum. They are typically configured to have a probe pierce the septum to provide a flow of sparging gas from the sample headspace of the vial to the entrance of an analytical instrument, for analysis of the headspace.
Headspace analysis is a technique in which a gas that has previously been in contact with a sample in a condensed phase (solid, liquid, or semi-solid) is examined for the presence of volatile compounds released into the gas. The partitioning of analytes into the gas phase may be understood or even predicted with thermodynamic considerations. This thermodynamic relationship may sometimes make possible the approximation of analyte concentration in the original condensed phase. Headspace analysis may typically be easily accomplished for volatile analytes in a nonpolar matrix. Other sample presentations may be more difficult with known headspace sampling devices.
Sampling methods from headspaces may be either static or dynamic. In static methods, one typically pressurizes a sealed vial or vessel containing the condensed analyte (to slightly above atmospheric pressure), then sampling may be done of the pressurized headspace through a septum. Sampling may be done with a gas tight syringe (with or without a syringe valve), a multiport sampling valve, or with a solid phase microextraction (SPME) fiber. In dynamic methods, a flow of carrier or sweep gas may be applied to the matrix containing the analyte. The stream may then be collected in a cryostat, adsorbent or solvent, thus this method is often referred to as purge and trap. The sweep gas may be under a positive pressure or drawn through the sample at reduced pressure.
When the analyte in the headspace gas is at a trace level, or when an exhaustive analysis of all constituents is desired, purge and trap methods are often preferred over static headspace or even modern SPME approaches. For analytes of very low volatility, longer collection times are required to collect sufficient sample for analysis. One means of obtaining a sample and introducing it into an analytical instrument, such as a chromatographic column, is known as “headspace sampling”. In conventional headspace sampling, sample material is sealed in a vial and subjected to constant temperature conditions for a specified time. Analyte concentrations in the vial gas phase should reach equilibrium with the liquid and/or solid phases during this thermostatting time. The vial is subsequently pressurized with carrier gas to a level greater than the “natural” internal pressure resulting from thermostatting and equilibration. Then the pressurized vial is connected to the chromatographic column in such a way as to allow for the transfer of a portion of the vial gas phase into the column for a short period of time.
A technique for delivering sample vapor to an analytical instrument is a ‘purge and trap’ apparatus. A purge and trap apparatus is used for capturing and identifying volatile organic compounds in a sample. Purge and trap system are configured for sparging liquid or solid samples containing volatile organic compounds at a controlled temperature with a regulated flow of inert gas for a fixed period of time. Sparging gas enters through a needle adaptor and passes through a sparging needle which is inserted into a vial containing a sample therein.
Gas chromatography is one of the most common analytical instruments used for the separation of compounds for the purpose of purification, identification, and quantification. The sparging gas passes through the sample and strips analytes from the sample which are accumulated and concentrated on a cool sorbent trap. The sorbent trap comprises a stationary phase or material suitable to collect the material to be accumulated for analysis. The trap functions as a sample concentrator which thermally traps and selectively later desorbs organic compounds for analysis.
After the material of interest is accumulated in the trap, the trap is then rapidly heated. The analytes are then desorbed from the trap as a plug and are moved by a flow of carrier gas which passes into the gas chromatograph. The gas chromatograph provides an output indicative of the substances in the sample. The sample is swept through the column by an inert carrier gas. After passing through the column, the separated solutes flow through a detector the output of which is displayed on a recorder or computer.